1. Field of Invention
The present invention relates to an improved method of, and a disposable test measurement instrument for, determining the Erythrocyte (or red blood cell) Sedimentation Rate (ERS) of a sample of anti-coagulated whole blood, in a safe, effective and inexpensive manner within diverse clinical settings.
2. Brief Description of the State of Knowledge in the Art in the Field of Invention
In 1894, Edmund Biernacki (1866-1912), a Polish physician, first noted the increased sedimentation rate of blood from ill individuals and realized that this increase was due to the presence of fibrinogen in the individual's blood sample.
In 1918, Robin Fahraeus (1888-1968) furthered Biernacki's work. His initial motivation to study the ESR of blood was as a pregnancy test, but his interest expanded to the study of the ESR test in disease states of his patients.
In 1921, Alf Westergren (1881-1968) refined the technique of performing the ESR test and reported its usefulness in determining the prognosis of patients with tuberculosis.
In 1935, Maxwell M. Wintrobe (1901-1986) published a variation of the ESR methodology and, at one time, this method was in wide use.
In 1977, the International Committee for Standardization in Hematology (ICSH) recommended the adoption of the Westergren method as the worldwide standard of ESR testing.
In 1997, the NCCLS published the ICSH's most recent recommendations on ESR Testing in the NCCLS Publication No. H2-A4 entitled “Reference and Selected Procedure For The Erythrocyte Sedimentation Rate (ESR) Test; Approved Standard (Fourth Edition), incorporated herein by reference in its entirety.
Also, NCCLS has recently published a number of other important documents setting forth standards and guidelines in relation to ESR testing, namely: No. C28-A2 entitled “How to Define and Determine Reference Intervals in the Clinical Laboratory” which sets forth standard guidelines for determining reference values and reference intervals for quantitative clinical laboratory tests; No. H1-A4 entitled “Evacuated Tubes and Additives for Blood Specimen Collection” which sets forth standard requirements for blood collection tubes and additives including heparin, EDTA, and sodium citrate; No. H3-A4 entitled “Procedures for the Collection of Diagnostic Blood Specimens by Venipuncture” which sets forth standard procedures for the collection of diagnostic specimens by venipuncture, including line draws, blood culture collection, and venipuncture in children, and also includes recommendations on order of draw; No. H7-A3 entitled “Procedure for Determining Packed Cell Volume by the Microhematocrit Method” which sets forth the standard microhematocrit method for determining packed-cell volume, and addresses recommended materials and potential sources of error; No. H18-A2 entitled “Procedures for the Handling and Processing of Blood Specimens” which addresses the multiple factors associated with handling and processing specimens, as well as factors that can introduce imprecision or systematic bias into results; and also No. M29-A entitled “Protection of Laboratory Workers from Instrument Biohazards and Infectious Disease Transmitted by Blood, Body Fluids and Tissue” which sets forth guidance on the risk of transmission of hepatitis viruses and human immunodeficiency viruses in any laboratory setting, specific precautions for preventing the laboratory transmission of blood-borne infection from laboratory instruments and materials, and recommendations for the management of blood-borne exposure. Each of these NCCLS documents helps to indicate the state of knowledge in the art in this field, and is incorporated herein by reference in its entirety.
Today, the Erythrocyte Sedimentation Rate (ESR or Sed Rate) test is one of the most widely performed laboratory tests throughout the world, used to help screen for general illness by determining if a patient has a condition which is causing acute or chronic inflammation, indicated by elevated levels of fibrinogen in the patent's blood. While the ESR test is non-specific, it is still very helpful in following the course of some inflammatory diseases.
The Westergren ESR test method, which is the “Gold Standard” reference method for the ESR test, is performed by placing a diluted sample of anti-coagulated blood in a tall, perfectly vertical tube of 2.5 mm diameter and 200 mm length, and measuring how far in [mm/hr] the blood plasma/erythrocyte cell (P/E) interface level has settled under the influence of gravitational forces after the lapse of sixty (60) minutes (i.e. one hour). The collected whole blood sample is prevented from coagulation by the addition of K3EDTA, and the anti-coagulated blood sample is then diluted by adding four parts of whole anti-coagulated blood to one part dilutent (such as physiologic saline or trisodium citrate at a concentration of between 0.10 to 0.136 mol/litre). The test works because the proteins associated with inflammation, particularly fibrinogen, counteract the zeta potential of red blood cells, which is created by a negative surface charge on the erythrocytes. This negative charge on the erythrocytes serves to repel the individual erythrocytes from each other and thus prolong erythrocyte sedimentation. When systemic inflammation is present, the fibrinogen content of the blood increases, and the erythrocytes tend to aggregate, thereby decreasing their surface-to-mass ratio, and thus increasing their rate of sedimentation.
The Wintrobe ESR test method employs a shorter tube (100 mm) than that used in the Westergren ESR method, and also a different anti-coagulant (i.e. ammonium oxide and potassium oxalate) in smaller amounts so as to not function as a diluting agent. It is generally accepted that the Wintrobe method is more sensitive for mild elevations, but also has a higher false positive rate than the Westergren method. On the other hand the Westergren method is more sensitive for changes at the elevated levels and more useful where the ESR test is being used to evaluate the response to therapy, i.e. in diseases such as temporal arteritis.
Various types of prior art apparatus have been proposed for performing the ESR test using manual principles of operation. The following Patents describe such form of apparatus: U.S. Pat. No. 5,914,272; U.S. Pat. No. 5,779,983; U.S. Pat. No. 5,745,227; U.S. Pat. No. 5,244,637; U.S. Pat. No. 5,065,768; U.S. Pat. No. 4,701,305; U.S. Pat. No. 4,622,847; U.S. Pat. No. 4,434,802; U.S. Pat. No. 4,353,246; U.S. Pat. No. 4,187,719; U.S. Pat. No. 3,938,370; U.S. Pat. No. 3,910,103; U.S. Pat. No. 3,660,037; U.S. Pat. No. 3,373,601; UK Application No. GB 2 116 319 A; and UK Application No. GB 2 048 836 A, each patent being incorporated herein by reference.
However, the ESR test instrumentation disclosed in the above prior art references generally involves the handling of blood in a less than satisfactory manner, creates unnecessary risks to those performing the measurements and to those disposing of the collected blood samples, and requires the lab technician to possess a relatively high degree of skill and dexterity if the test results are to be measured accurately.
Various approaches to automating the ESR test have been attempted, notably using electronic and optical means for tracking the sedimentation of the erythrocytes and providing a result in less than the usual sixty minutes. Such techniques are illustrated in U.S. Pat. Nos. 5,914,272; No. 5,575,977; No. 5,316,729; No. 4,801,428; No. 4,744,056; No. 4,187,462; and No. 4,041,502, each being incorporated herein by reference.
While these prior art methods and apparatus have reduced ESR test times substantially below the standard 60 minute test time period, the results produced by such prior art methods and apparatus do not correlate well with the “reference” Westergren ESR method, and involve the use of expensive equipment.
Thus, there is a great need in the art for an improved method of and apparatus for measuring the rate of erythrocyte sedimentation in a sample of whole blood, while avoiding the shortcomings and drawbacks of prior art apparatus and methodologies.